1. Field of the Invention
The present invention relates to a photoelectric conversion device, and more particularly to a photoelectric conversion device suitable for use with scanners, video cameras, digital still image cameras.
2. Related Background Art
If incidence light oblique to the substrate of a photoelectric conversion device reaches a photoelectric conversion area directly or in multiple reflection, there arises a problem of malfunction or image deterioration. For example, in a photoelectric conversion device made of a plurality of unit pixels disposed in two-dimensionally, if oblique incidence light to some pixel enters adjacent pixels directly or in multiple reflection, there arise problems of degraded resolution and the like. It is therefore desired to prevent light leakage by forming a light shielding region or a light absorption region between adjacent pixels.
In forming a photoelectric conversion device having a number of fine unit pixels, such as an image pickup photoelectric conversion device, it is desired to reduce the ratio of the area occupied by a light shielding region in each unit pixel. This is because the smaller the area of a light shielding region in each unit pixel, the area ratio (hereinafter called an opening ratio) of the photoelectric conversion area in each unit pixel can be made larger so that a light sensitivity can be prevented from being lowered.
FIG. 8A shows the structure similar to that of a photoelectric conversion device described in JP-A-4-91472. In FIG. 8A, reference numeral 20 represents a semiconductor substrate, reference numeral 21 represents an n+-type buried layer, reference numeral 22 represents an nxe2x88x92-type epitaxial layer, reference numeral 23 represents an n+-type element separation region, reference numeral 24 represents a photoelectric conversion region constituting a dark pixel, reference numeral 25 represents a light shielding for preventing light from entering the photoelectric conversion region from the upper side or oblique upper side, and reference numeral 26 represents an insulating layer.
The upper area and upper peripheral area of the photoelectric conversion region 24 surrounded by the n+-type buried layer 21 and n+-type element separation region 23 are covered with the light shielding 25. Since incidence light from the upper side and oblique upper side can be shielded, the photoelectric conversion region 24 of the dark pixel can output a dark current always stably without being influenced by the external light state.
FIG. 8B is a schematic top view of another photoelectric conversion device. In FIG. 8B, reference numeral 41 represents an anode of a photodiode constituting a photoelectric conversion region, reference numeral 42 represents a cathode, reference numeral 43 represents a light shielding for preventing oblique light from being entered, and reference numeral 50 represents a contact hole connected to a transistor constituting a unit pixel. In order to make finer a unit pixel constituted of at least the photoelectric conversion region 41 and contact hole 50 and not to lower the opening ratio, it is desired to form the contact hole 50 and light shielding 43 as near as possible. However, if the light shielding 43 and contact hole 50 are formed near at each other to make the pixel finer, by photolithography using a phase shift method and anisotropic etching, diffraction light applied to mask patterns for the light shielding 43 and contact hole 50 may cause interference and desired resist patterns may not be formed. From this reason, it is necessary to broaden a space therebetween or to form the light shielding 43 and contact hole 50 not by the same process but by different processes.
However, if a space between the light shielding 43 and contact hole 50 is made large, the opening ratio lowers opposing the current tendency of making a unit pixel finer.
It is an object of the invention to provide a photoelectric conversion device capable of suppressing deterioration of a resolution to be caused by incidence of oblique light and/or multiple reflection light into a photoelectric conversion region.
It is another object of the present invention is to provide a photoelectric conversion device capable of forming a light shielding and a contact hole near at each other.
According to one aspect of the invention, there is provided a photoelectric conversion device comprising: a substrate; a light reception area formed on a surface of the substrate, the light reception area having at least one unit pixel; an insulating layer formed on the substrate including the light reception area; and a light shielding group made of a plurality of light shieldings and formed through the insulating layer along a direction perpendicular to the substrate, the light shielding group surrounding a unit pixel or the light reception area.